DECOMPOSITION AND NUTRIENT DYNAMICS OF REED (PHRAGMITES-AUSTRALIS (CAV) TRIN EX STEUD) LITTER IN LAKE NEUSIEDL, AUSTRIA

Common reed leaf and stalk litters were exposed in coarse (5 mm) and fine (70 mum) mesh bags at five sites from the landward to the lakeward margin of the reed belt of Lake Neusiedl, Austria. Additionally, some samples were exposed above water and in a reedless pool. After 863 days, leaves exposed below water had lost 51-85% of the original ash-free dry weight, depending on site and bag mesh size. Weight losses of stalks and of litter exposed above water were considerably smaller (15-32%). Decomposition was fastest at the lakeward site, slowest in the middle of the reed belt, and intermediate at the landward site. This rate correlated with concentrations of N, P, K and Ca, which were high after a short time in the litter at sites with higher decomposition rates. Leaves collected from one site and exposed at others showed that decomposition rates depended on site characteristics rather than on initial litter quality. Nutrient concentrations (N, P, K, Na, Ca and Mg), except of Fe, decreased during the first month, and all, including Fe, increased subsequently until the end of the study period. Changes of cation concentrations can generally be explained by cation exchange processes. Photosynthesis of epiphytes, carbonate precipitation and sediment incorporation can account for some of the changes observed. Increases in N and P, in contrast, seem to be controlled mainly by uptake by litter-settling micro-organisms. Of the various mathematical models tested, one including a temperature-independent labile fraction and a temperature-dependent recalcitrant fraction was the most successful.